This invention relates to nuclear reactors, and in particular to that kind of nuclear reactor known as a liquid metal cooled fast breeder reactor in which a core composed of fuel elements is disposed within a tank containing liquid metal and heat generated in the core is extracted by liquid metal flowing between the core and one or more heat exchangers, the tank being housed in a vault provided with a roof in which rotatable shields are mounted, allowing fuel elements to be charged into and discharged from the core when necessary.
The vault roof and the rotatable shields therein constitute the main shielding above the reactor core and protect operators and equipment. To fulfill their support and shielding function properly, the roof and shields require to be cooled in a manner such that an acceptable temperature gradient from inside to outside is set up. Hitherto, cooling of the roof and shields has been by flowing coolant therethrough, with the rotating shield coolant inlet and outlet pipe work situated above the roof and shields. This pipework takes up valuable space above the roof and is prone to accidental damage during reactor component removal. Furthermore, when refuelling is necessary, the coolant connections to the shields have to be broken to allow rotation, and temporary cooling of the shields by forced circulation of ambient air has been necessary, which adds further complication to the refuelling operation.